Thiophene derivative polymer and a polymer composition thereof

ABSTRACT

A thiophene derivative polymer comprising repeating units of the formula: ##STR1## (wherein R stands for one member selected from the group consisting of ##STR2## and a polymer composition having the polymer doped with an anion and consequently possessing a semiconducting characteristic.

This is a division of application Ser. No. 07/155,274, filed Feb. 12,1988.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel thiophene derivative polymer and athiophene derivative polymer composition obtained by doping the polymerwith an anion. The polymer composition exhibits electric propertieswhich make it suitable as a semiconductor. Further, the polymercomposition and the polymer possess special colors.

2. Prior Art Statement

In recent years, display devices have come to play an important role asinput and output means. The most widely used type of display device usesa video tube. Such tubes, however, have a disadvantage in that they havelarge size and weight and consume much electric power. As a consequence,liquid crystal displays and electrochromic displays have been studiedand developed to take the place of video tubes.

In parallel with this electronic technology is being incorporated inmany kinds of equipment. As a result, such equipment can be reduced insize and improved in performance. The success in the incorporation ofelectronic technology is ascribable in a great measure to thedevelopment of semiconductors, integrated circuits, and LSI's. Displaymaterials and electronic materials are expected to find expandingapplications and demand for such materials is expected to grow in thefuture. Thus the development of new semiconductor materials is importantand studies are being continued on both organic and inorganic materials.Macromolecular semiconductors are therefore being studied because oftheir potentially extensive utility.

Heretofore, as macromolecular semiconductors, such polymers aspolyacetylene and polyphenylene to which a semiconducting property isimparted by the incorporation of an electron acceptor [Journal of theAmerican Chemical Society, Vol. 100, page 1013 (1978) and SyntheticMetal, Vol. 1, page 307 (1980)] and poly(3-methylthiophene) doped withan anion [Synthetic Metal, Vol. 14, page 279 (1986)] have been known tothe art.

These organic semiconductors are generally deficient in stability andheat-resisting property and, therefore, can be used only in limitedapplications. Since they emit colors only in limited hues when used indisplays, their utility in this field is also limited.

Polyacetylenes are highly susceptible to the action of oxygen andinstable in the air. They thus have a problem from the standpoint ofpractical use. Doped polymer of poly(3-methylthiophene) can be easilyobtained in the form of a film on the surface of an electrode by theelectrolytic polymerization process. The film thus obtained, however,needs further improvement because it does not have a smooth surface andis low in heat-resisting property.

Polythiophene heretofore used as an electrochromic display material canemit only two hues, red in the neutral state and blue when doped with ananion [Japanese Journal of Applied Physics, Vol. 22, page 412 (1983)].

OBJECT AND SUMMARY OF THE INVENTION

An object of this invention is to provide a novel organic semiconductorwhich exhibits stability in the air, enjoys improvement inheat-resisting property and smoothness of film, and emits colors in awide variety of hues.

The inventors continued a study for developing an organic semiconductoranswering the foregoing description. They have found, as the result,that a polymer composition produced by doping with an anion a polymerwhich has as a repeating unit thereof a group containing anotherheterocycle to be interposed between adjacent thiophene rings possessesa semiconducting characteristic. They have further confirmed that thiscomposition and the polymer both emit peculiar colors of their own. Thisinvention has been perfected as a result.

Specifically, this invention is directed to a thiophene derivativepolymer comprising repeating units represented by the formula: ##STR3##(wherein R stands for one member selected from the group consisting of##STR4## and to a polymer composition obtained by doping theaforementioned polymer with an anion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polymer and the polymer composition of the present invention arenovel substances not published in any literature. The polymer which isin a neutral state and the polymer composition which is produced bydoping this polymer with an anion and consequently is in an oxidizedstate possess peculiar colors, depending on their respective states, andcan be utilized as display materials. They are electrical insulators intheir neutral state and assume a semiconducting property in theiroxidized state.

As examples of the anion with which the polymer can be doped effectivelyin this invention, there can be cited tetrafluoroborate ion, perchlorateion, hexafluorophosphate ion, hexafluoroarsenate ion, iodine ion,bromine ion, chlorine ion, fluorine ion, sulfate ion, hydrogensulfateion, trifluoroacetate ion, and p-toluenesulfonate ion.

The polymer and the polymer composition of the present invention arenovel compounds. They are insoluble in solvents and, when heated, aredecomposed instead of being dissolved. Thus, their molecular weights andpolymerization degrees are very difficult to determine. Thepolymerization degrees are thought to fall roughly in the range of 10 to500 and the molecular weights in the range of 2,000 to 100,000.

The polymer of this invention, whether in an oxidized state (polymercomposition) or in a neutral state, assumes hues different frompolythiophene and, therefore, can be used as a display material.

Polythiophene in a neutral state assumes a red color and in a statedoped with tetrafluoroborate ion, for example, assumes a blue color.

The polymer of this invention having ##STR5## as the substituent Rassumes a yellow color and the polymer composition obtained by dopingthis polymer with tetrafluoroborate ion assumes a brown color.

The polymer having ##STR6## as the substituent R assumes a yellowishorange color and the polymer composition obtained by doping this polymerwith tetrafluoroborate ion assumes a grayish black color.

The polymer having ##STR7## as the substituent R assumes a brown colorand the polymer composition obtained by doping this polymer assumes ablackish brown color.

The polymer composition exhibits electroconductivity ranging from 10⁻⁵up to 10⁻² S/cm and high stability to the air and, therefore, can beapplied as an electromagnetic wave-shielding material, electrodematerial, and solar cell material.

The film made of the polymer having ##STR8## as the substituent Rpossesses a smooth surface and excels in heat-resisting property.

Further, the polymer composition possesses the following characteristicproperties as an organic semiconductor.

While the polymer by itself is an insulator, the polymer compositionobtained by doping the polymer with an anion assumes a positive electriccharge and, therefore, exhibits the properties of a semiconductor. Theelectroconductivity of the polymer composition is in the range of 10⁻²to 10⁻⁵ S/cm.

The polymer composition exhibits practically desirable properties whenthe anion content thereof is in the range of 10 to 50% by weight.

The polymer and the polymer composition have been identified by means ofinfrared absorption spectrum.

Now, the method used for the production of the polymer and the polymercomposition will be described below.

The polymer of the present invention can be produced by subjecting acompound of the formula: ##STR9## or a compound of the formula:##STR10## or a compound of the formula: ##STR11## to electrolyticpolymerization.

The electrolytic polymerization is carried out in the presence of asupporting electrolyte. The product of the electrolytic polymerizationis doped with an anion originating in the supporting electrolyte. Thus,this product is a polymer composition.

When this product is electrolyzed with the polarity reversed, thethiophene derivative polymer aimed at by this invention is obtained in astate deprived of the dopant.

Advantageously, the electrolytic polymerization is carried out in apolar solvent under the atmosphere of an inert gas. As examples of thepolar solvent which proves to be favorable for the electrolyticpolymerization, there can be cited acetonitrile, nitrobenzene,nitromethane, benzonitrile, propylene carbonate, tetrahydrofuran,methylene chloride, dimethyl sulfoxide, dimethyl formamide,hexamethylphosphor triamide, 1-methyl-2-pyrrolidinone, dimethyl sulfate,and diethyl sulfate. As the inert gas for the atmosphere of theelectrolytic polymerization, nitrogen, argon, or other inert gas isused. By carrying out the reaction under the atmosphere of such an inertgas, the intermediate of the reaction can be prevented from reactingwith oxygen and consequently giving rise to a secondary product.

As the electrode, besides such precious metal as gold or platinum, aglass electrode produced by vacuum depositing indic oxide or stannicoxide on the surface of glass sheet can be used.

As examples of the supporting electrolyte effectively usable herein,there can be cited tetramethyl ammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, tetra-n-butyl ammonium tetrafluoroborate,lithium tetrafluoroborate, tetramethyl ammonium perchlorate, tetraethylammonium perchlorate, tetra-n-butyl ammonium perchlorate, lithiumperchlorate, tetramethyl ammonium hexafluorophosphate, tetra-n-butylammonium hexafluorophosphate, sodium hexafluorophosphate, tetra-n-butylammonium hexafluoroarsenate, sodium hexafluoroarsenate, sulfuric acid,tetramethyl ammonium hydrogen sulfate, tetra-n-butyl ammonium hydrogensulfate, sodium trifluoroacetate, tetramethyl ammoniump-toluenesulfonate, and tetra-n-butyl ammonium p-toluenesulfonate.

The compound of the aforementioned formula (II) is a novel compound andis synthesized by causing magnesium metal to react with 2-bromothiophenethereby producing a Grignard reagent and then condensing the Grignardreagent in combination with 2,5-dibromothiazole.

The compound of the aforementioned formula (III) is likewise a novelcompound and is synthesized by causing magnesium metal to react with2-bromothiophene thereby producing a Grignard reagent and thencondensing the Grignard reagent in combination with 2,5-dibromopyridine.

The concentration of the supporting electrolyte in the solvent is in therange of 0.01 to 1 mol/liter. If this concentration is less than thelower limit of this range, the electrolysis does not proceed smoothly.If the concentration exceeds the upper limit, then there is thepossibility of impurities in the supporting electrolyte adverselyaffecting the polymerization.

The concentration of the monomer subjected to polymerization in thesolvent system is in the range of 0.01 to 1 mol/liter.

The thiophene derivative polymer composition of the present invention isobtained by dissolving a thiophene derivative and a supportingelectrolyte in a solvent and subjecting the resultant solution toelectrolytic polymerization. This production is characterized by thefact that the polymerization of the monomer and the doping of thepolymer are attained substantially by one step. When the product isfurther electrolyzed with the polarity reversed, the dopant is easilyremoved and the thiophene derivative polymer is obtained. The polymer orthe polymer composition is obtained in the form of film deposited on thesurface of the electrode. Since the thickness of the produced film canbe adjusted by the amount of electricity fed to the electrolytic cell,no molding is required.

Now, the present invention will be described more specifically belowwith reference to working examples. Referential Example 1 (Production of2,5-di(2-thienyl)thiazole:

When a three-neck 50-ml flask fitted with a reflux condenser, a stirrer,and a calcium chloride tube was charged with 6.45 g (40 m.mols) of2-bromothiophene and 29 ml of dehydrated ether and then 1.06 g (44m.mole) of a magnesium metal was added thereto, the resultant reactionmixture produced 2-thienyl magnesium bromide with evolution of heat.Under an atmosphere of nitrogen, 4.0 g (16 m.mols) of2,5-dibromothiazole, 0.179 g (0.33 m.mol) ofdichloro[1,3-bis(diphenylphosphino)propane] nickel, and 29 ml ofdehydrated ether were added to the 2-thienyl magnesium bromide. Theresultant mixture was placed and refluxed for 16 hours in a three-necked100-ml flask fitted with a reflux condenser, a stirrer, and a calciumchloride tube. The reaction mixture was treated with 1N hydrochloricacid and the water layer separated from the organic layer was extractedwith ether. The organic layer was added to the water layer extractedwith ether. The resultant liquid was washed with water, cleaned with asaturated aqueous sodium hydrogen carbonate solution, and then washedagain with water. The washed liquid layer was dried with anhydroussodium sulfate, treated with activated carbon, and recrystallized twicewith n-hexane, to produce 237 mg (5.8%) of yellow leaflike crystals of2,5-di(2-thienyl)thiazole having a melting point of 93.0° to 93.8° C.

Elementary analyses (as C₁₁ H₇ NS₃); Calculated - C 52.98%, H 2.83%, N5.62%, S 38.57%; Found - C 53.05%, H 2.51%, N 5.55%, S 38.54%

Referential Example 2 (production of 2,5-di(2-thienyl)pyridine):

2,5-di(2-thienyl)pyridine was obtained by following the procedure ofReferential Example 1, except that 2,5-dibromopyridine was used in theplace of 2,5-dibromothiazole. This product was recrystallized withethanol, to obtain light yellow needle crystals having a melting pointof 149.5° to 150.5° C.

Elementary analyses (as C₁₃ H₉ NS₂); Calculated - C 64.17%, H 3.73%, N5.76%, S 26.35%; Found - C 64.19%, H 3.49%, N 5.70%, S 26.30%

EXAMPLE 1

In an electrolytic cell having a platinum plate (1×1=1 cm²) as a cathodeand a glass electrode (1×1=1 cm²) an anode disposed as separated by 1cm, 62 mg (0.25 m.mol) of 2,5-di(2-thienyl)thiazole, 82 mg (0.25 m.mol)of tetra-n-butyl ammonium tetrafluoroborate, and 5 ml of propylenecarbonate were placed and dissolved. The solution was blown with argonfor 15 minutes and then subjected to electrolytic polymerization at acurrent density of 1 mA/cm² and a polymerization temperature of 25° C.for 30 seconds. Consequently, a brown film of polymer composition dopedwith tetrafluoroborate ion was obtained on the anode. The film had athickness of about 0.2 μm. When this polymer composition was furtherelectrolyzed, with the polarity reversed, at a current density of 0.1mA/cm² and a temperature of 25° C. for 30 seconds, the composition wasdeprived of tetrafluoroborate. Consequently, there was obtained a yellowfilmlike polymer.

In the infrared absorption spectrum of the yellow filmlike polymer,there was found a band at 800 cm⁻¹ indicative of the presence of2,5-di-substituted thiophene ring. The bands at 730 and 820 cm⁻¹indicative of the presence of a 2,4-di-substituted thiophene ring wereabsent from this infrared absorption spectrum. Thus, the polymer wasidentified to be the polymer of ##STR12##

EXAMPLE 2

In an electrolytic cell having two platinum plates (1×1=1 cm²) disposedas separated by 1 cm, 62 mg (0.25 m.mol) of 2,5-di(2-thienyl)thiazole,82 mg (0.25 m.mol) of tetra-n-butyl ammonium tetrafluoroborate, and 5 mlof propylene carbonate were placed and dissolved. The resultant solutionwas blown with argon for 15 minutes and then subjected to electrolyticpolymerization at a current density of 1 mA/cm² and a polymerizationtemperature of 25° C. for 2 hours. Consequently, a blackish brownfilmlike polymer composition doped with tetrafluoroborate ion wasobtained as deposited on the anode. This film had a thickness of 18 μm.It showed electroconductivity of 6.3×10⁻⁵ S/cm.

EXAMPLE 3

In an electrolytic cell having two glass electrodes (1×1=1 cm²) disposedas separated by 1 cm, 122 mg (0.5 m.mol) of 2,5-di(2-thienyl)pyridine,82 mg (0.25 m.mol) of tetra-n-butyl ammonium tetrafluoroborate, and 5 mlof nitrobenzene were placed and dissolved. The resultant solution wasblown with argon for 15 minutes and then subjected to electrolyticpolymerization at a current density of 1 mA/cm² and a polymerizationtemperature of 25° C. for 1 minute. Consequently, a grayish blackfilmlike polymer composition doped with tetrafluoroborate ion wasobtained as deposited on the anode. This film had a thickness of about 1μm. When this polymer composition was further electrolyzed, with thepolarity reversed, at a current density of 1 mA/cm² and a temperature of25° C. for 60 seconds, the composition was deprived oftetrafluoroborate. Thus, there was obtained a yellowish orange filmlikepolymer.

In the infrared absorption spectrum of this yellowish orange filmlikepolymer, there was found a band at 800 cm⁻¹ indicative of the presenceof 2,5-di-substituted thiophene ring. The bands at 730 and 820 cm⁻¹indicative of the presence of a 2,4-substituted thiophene ring wereabsent from this infrared absorption spectrum. Thus, this polymer wasidentified to be the polymer of ##STR13##

EXAMPLE 4

In the same electrolytic cell as described in Example 1, 122 mg (0.5m.mol) of 2,5-di(2-thienyl)pyridine, 82 mg (0.25 m.mol) of tetra-n-butylammonium tetrafluoroborate, and 5 ml of nitrobenzene were placed anddissolved. The resultant solution was blown with argon for 15 minutesand then subjected to electrolytic polymerization at a current densityof 1 mA/cm² and a polymerization temperature of 25° C. for 5 minutes.Consequently, a grayish black filmlike polymer composition doped withtetrafluoroborate ion was obtained as deposited on the anode. When thispolymer composition was further electrolyzed, with the polarityreversed, at a current density of 1 mA/cm² at a temperature of 25° C.,it was deprived of the dopant. Consequently, there was obtained areddish brown filmlike polymer. When this filmlike polymer was exposedto the vapor of iodine, there was obtained a polymer doped with iodineion. This polymer showed electroconductivity of 6.0×10⁻³ S/cm.

EXAMPLE 5

In the same electrolytic cell as described in Example 1, 122 mg (0.5m.mol) of 2,5-di(2-thienyl)pyridine, 85 mg (0.25 m.mol) of tetra-n-butylammonium perchlorate, and 5 ml of nitrobenzene were placed anddissolved. The resultant solution was blown with argon for 15 minutesand then subjected to electrolytic polymerization at a current densityof 1 mA/cm² and a polymerization temperature of 25° C. for 5 minutes.Consequently, a grayish black filmlike polymer composition doped withperchlorate ion was obtained as deposited on the anode. When the polymercomposition was further electrolyzed, with the polarity reversed, at acurrent density of 1 mA/cm² and a temperature of 25° C., there wasobtained a reddish brown filmlike polymer deprived of the dopant.

EXAMPLE 6

In the same electrolytic cell as described in Example 3, 122 mg (0.5m.mol) of 2,6-di(2-thienyl)pyridine, 82 mg (0.25 m.mol) of tetra-n-butylammonium tetrafluoroborate, and 5 ml of nitrobenzene were placed anddissolved. The resultant solution was blown with argon and thensubjected to electrolytic polymerization at a current density of 1mA/cm² and a polymerization temperature of 25° C. for 2 minutes.Consequently, a blackish brown filmlike polymer composition doped withtetrafluoroborate ion was obtained as deposited on the anode. Thisfilmlike polymer composition had a thickness of about 1 μm. When thispolymer composition was further electrolyzed with the polarity reversed,there was obtained a brown polymer deprived of the dopant.

In the infrared absorption spectrum of the brown filmlike polymer, aband at 800 cm⁻¹ indicative of the presence of a 2,5-di-substitutedthiophene ring was observed. The oands at 730 and 820 cm⁻¹ indicative ofthe presence of a 2,4-di-substituted thiophene ring were not found.Thus, the polymer was identified to be the polymer of ##STR14## The filmof this polymer had a very smooth surface. The surface smoothness ofthis film was higher than that of any other film obtained byelectrolytic polymerization as reported in literature to date. Table 1shows the results of thermogravimetric analysis of the polymer ascompared with that of poly(3-methylthiophene).

                  TABLE 1                                                         ______________________________________                                        Gravimetric residual ratio of polymer (%)                                     ______________________________________                                        Temperature (°C.)                                                                       200    300    400  500  600                                  Poly[ 2,6-di(thienyl)pyridine]                                                                 100    100    99   99   94                                   Poly(3-methylthiophene)                                                                        100    98     96   90   73                                   ______________________________________                                    

From this table, it can be clearly noted that the polymer showed betterthermal stability than poly(3-methylthiophene), a substance heretoforeaccepted as possessing relatively high stability.

EXAMPLE 7

In the same electrolytic cell as described in Example 1, 122 mg (0.5m.mol) of 2,6-di(2-thienyl)pyridine, 82 mg (0.25 m.mol) oftetra-n-ammonium tetrafluoroborate, and 5 ml of nitrobenzene were placedand dissolved. The resultant solution was blown with argon for 15minutes and then subjected to electrolytic polymerization at a currentdensity of 1 mA/cm² and a polymerization temperature of 25° C. for 5minutes. Consequently, a blackish brown filmlike polymer compositiondoped with tetrafluoroborate ion was obtained as deposited on the anode.When this polymer composition was further electrolyzed with the polarityreversed, there was obtained a brown filmlike polymer deprived of thedopant. When this polymer was exposed to the vapor of iodine, it wasdoped with iodine ion. This polymer had an electroconductivity of1.3×10⁻² S/cm.

EXAMPLE 8

In the same electrolytic cell as described in Example 1, 122 mg (0.5m.mol) of 2,6-di(2-thienyl)pyridine, 97 mg (0.25 m.mol) of tetra-n-butylammonium hexafluorophosphate, and 5 ml of nitrobenzene were placed anddissolved. The resultant solution was blown with argon for 15 minutesand then subjected to electrolytic polymerization at a current densityof 1 mA/cm² and a polymerization temperature of 25° C. for 5 minutes.Consequently, a blackish brown filmlike polymer composition doped withhexafluorophosphate ion was obtained as deposited on the anode. Whenthis polymer composition was further electrolyzed with the polarityreversed, there was obtained a brown filmlike polymer deprived of thedopant.

What is clamied is:
 1. A thiophene derivative polymer composition,comprising:a polymer having repeating units of the formula: ##STR15##wherein n denotes a number within the range of about 10 to 500 and Rrepresents a member selected from the group consisting of ##STR16##doped with at least one anion selected from the group consisting of thetetrafluoroborate ion, perchlorate ion, hexafluorophosphate ion,hexafluoroarsenate ion, iodide, bromide, chloride, fluoride, sulfate,hydrogen sulfate, trifluoroacetate and p-toluenesulfonate in an amountwithin the range of 10 to 50% by weight.
 2. The thiophene derivativecomposition according to claim 1, wherein R is ##STR17##
 3. Thethiophene derivative composition according to claim 1, wherein R is##STR18##
 4. The thiophene derivative composition according to claim 1,wherein R is ##STR19##